Melting furnace



Dec. l5, 1931. s. w. CRAWFORD MELTING FURNACE Filed Jan. 22, 1931 3Sheets-Sheet 2 Dec. l5, 1931. s. w. CRAWFORD IELTING FURNAGE f FiledJan. '22, 1931 3 Sheets-Sheet 3 Patented Dec. 15, 1931 UNITED STATESPATENT OFFICE SAMUEL W. CRAWFORD, OF ST. LOUIS, MISSOURI, .ASSIGNOR TONATIONAL BEARING METALS CORPORATION, OF ST. LOUIS, MISSOURI, ACORPORATION OI? NEW YORK MELTIN G FURNACE Application led January 22,1931. Serial No. 510,478.

This invention relates generally to melting furnaces, and moreparticularly to an improved method and means 'for melting bronze orallied alloys or their metals.

One of the difficulties encountered in this art is that the admittanceof air at the comparatively cold ordinary temperatures to the tuyres ofthe furnace tends to chill and thicken the slag so that the latterretards l the distribution of the air through the fuel mass.Furthermore, the warmer the air that is admitted to the tuyres, thesmaller may be the proportion of fuel to metal in charging the furnace.The time required to melt the metal is, also, reduced. Accordingly, onepurpose of the present inventionlis to provide means for preheating theair before it enters the tuyres. p

Another purpose 'is to lpreheat the air by utilizing the heat of thegases in the furnace that ordinarily passes out ofV the furnace With thegases into the atmosphere and is thereby ordinarily wasted.

Another object is to provide a reducing atmosphere in Jthe furnacesufficient to prevent oxidation of the'metal and the undue formation ofslag.

A further object of the invention is the provision of a method offeeding the charges of metal and fuel to the furance so as to provide acontinuous supply of molten metal at a desired uniform temperature.

Other objects, advantages and desirable features of the invention willappear in the course of the following description of an illustrativeembodiment of the spirit thereof.

In the accompanying drawings forming part of this specification, inwhich like numbers of reference denote like parts wherever they occur,

Figure 1 is an elevation of a furnace embodying the features of thepresent invention; f

Figure 2 is a fragmentary view similar to Figure 1, but on a largerscale, and with one lateral half of the view in vertical centralsection;l y

Figure 3 is a transverse sectional view taken on the line 3*?) in`Figure 2;

Figure 4t is a transverse sectional view taken on the irr-egular line 44 in Figure 2;

Figure 5 is a rear elevation of the air case employed in the furance toheat the air for the tuyres, showing the case detached;

Figure 6 is a fragmentary rear elevation of a modified form of air case;and

Figure 7 is a horizontal sectional view taken on the line 7 7 in Figure6.

The furnace shown is of the cupola type and comprises the usual outershell 1 of wrought iron `or steel plates riveted or otherwise securedtogether in any suitable manner, and the usual lining 2 of fire brick.The bottom may be formed as usual of two doors 3 Y opening downward andcovered on their n- 11 are provided in theinner face of the lining 2 toreceive the air-cases 12. The aircases 12 are arcuate in horizontalcross-section to conform to the recesses 11 in the annular lining 2, andthe inner wall 13 of each case 12 is corrugated to provide alternatevertically extending grooves 14 and ridges 15. The purpose of thecorrugations is to compensate for a difference of expansion between theinner wall 13 and the outer wall 16; and

to expose a greater surface to the interior of the furnace, therebyincreasing the heating capacity of the cases 12. The inner wall 13 andouter wall 16 of each case are secured together at intervals by stays17. The cases 12 are secured in position by T-shaped brackets 18, formedintegral with and projecting exteriorly from the wall 16, and riveted tothe shell 1. The upper and lower ends of each case 12 open outwardly orrearwardly, and are surrounded by rearwardly facing flanges 19, to whichare .attached the inwardly facing flanges 2O of an elbow pipe 21 and anelbow pipe 22 at the upper and lower ends respectively of each case 12.The cases 12 and the pipes 21 and 22 are preferably formed of cast iron.The elbows 21 and 22 extend through openings 23 and 24, respectively,provided therefor in the shell 1. The opening 23 is closed around theelbow 21 by a cover 25 suitably secured to the shell 1, as shown inFigures 6 and 7.

The lower vend of each elbow 22 is connected through the intermediacy ofa pipe 57 to an opening 26 in the top wall 27 'of a respective windbox28, that distributes the blast from the pipe 21 to each of a pluralityof tuyere boxes 29 through nipples 30 that are each connected at theirupper ends to a respective opening 31 in the lower wall 32 of thewindbox 28 and at their' lower ends to the opening 33 in the top wall 34of a respective tuyere box 29. Each of the tuyere boxes 29 is preferablyan iron casting, and its open inner end is provided with integralflanges 35 that are suitably'secured to the outer side of the shell 1 sothat the interior of the box communicates with a respective one of thetuyres 8. The outer wall 36 of each tuyere box 29 may be provided withclean-out doors 37, provided with observation openings 38. A jacket 39,preferably formed of steel plate, incloses the windbox 28, the part ofthe pipe 22 disposed exteriorly of the shell 1, and, also, the top wall34, bottom wall 40, and two lateral walls 41 of the tuyere boxes 297 aswell as closing the opening` 24 to the exterior of the furnace. Thewindbox 28 and the jacket 39 are preferably formed of plate steel, andare provided with suitable flanges 42 and 43, respectively, by means ofwhich they are secured to the outer side of the shell 1 by riveting orin any other suitable manner. The spaces 44 behind the cases 12 and overand under the same form passageways for thc heated asf cending gases;and the spaces 45 in the jaclret 39 are filled with a suitableinsulating mate rial 46, such a silocel, for retaining the heat in thecases 12 and in the elbows 22, windboxes 28, nipples 30, and tuyereboxes 29.

The blast for the tuyeres is supplied by a blower 47, driven by a motor48. The blower and motor are mounted upona suitable platform 49. A pipe50 leads from the discharge end 51 of the blower 47 and divides intobranches 52 and 53 that have their lower ends connected to the upperends of the elbows 21. The cross-section of the pipe 22 exceeds that ofthe pipe 21 sufficiently to compensate for the expansion of the heatedair.

If desired, the solid stays 17 may be supplanted by stays 58 of hollowor tubular formation, that will provide passageways 59 for conductingthe heated gases from the front side to the rear side of the air-cases12, as shown in Figures 6 and 7.

The construction of the furnace having been fully described, its mode ofoperation will be readily comprehended. The fuel bed is preferably builtup until its top is slightly higher than the top of the lining 9, cokebeing the usual and preferred fuel. After the ignition and usualpreliminary combus tion in the'fuel bed, the motor 48 is start-ed,thereby delivering a blast through the aircases 12 to the tuyres 8. Theascending gases in the furnace heat the air-cases 12, and thereby in ashort ywhile the air passing through the chambers 56 in the air-casesemerges from the tuyeres into the furnace at a temperature ranging fromthree hundred to five hundred degrees Fahrenheit. Vhen the fuel has beenbrought to the full or desired temperature,

and not until then, the first charge of metall is put en, then fuel ontop of the charge to an amount equal to that consumed per charge ofmetal. As soon as the first charge of metal has melted down until it isout of view of the operator, the next charge of metal and then the layerof coke on top of it is put on similarly to the manner in which thefirst charge was put on. These operations may be continually re-enactedto form a continuous process or supply of molten metal, since theintervals of the metal charges are such that each charge melts andmerges with the previous charge before the latter has been entirelydrawn out.

It has been ascertained that this process effects a twenty per cent.reduction in melting time, reducing it from about twelve to nineminutes, and furthermore effects a twenty-five per cent. saving in fuel.The temperature is governed by the depth of fuel under the metal charge;and about one hundred cubic feet of air is delivered for each pound ofcoke under three-fourths of an ounce to one ounce above normalatmospheric pressure. The heat absorbed by the air cases for preheatingthe blast is utilized between the tuyeres and the melting zone, where itis most effective, instead of passing out through the stack. The highertemperature produced by the preheated blast decreases the time ofmelting, and thereby the oxidation, which is especially important in themelting of non-ferrous metals such as bronze or brass or theirconstituents. Since the metal is not charged until the furnace is atfull temperature and the previous charge ias melted down, there is nooxidation prior to the short time of the actual melting of each charge,in contradistinction to the Voxidation that would occur if the furnacewere charged with alternate layers of coke and metal proior to theignition, as is customary in the operation of melting cast-iron.Furthermore, because of the hot blast and resulting higher temperaturein the melting zone, the percentage of carbon monoxide is materiallyincreased, which increases the reducing character of the gases in themelting zone and thereby further tends to reduce oxidation of the heatedmetal. Prior to the present invention, about ten per cent. of the volumeof the charge had become slag, which tends to chill and thicken andthereby retard the distribution of air through the fuel mass. When,however, the blast is preheated, the slag is materially reduced inamount, and, besides, being more highly heated, attains a greaterfluidity that offers less interference to the flow of the blast.

Having thus fully described this invention, I hereby reserve the benefitof all changes in form, arrangement, order, or use of parts, as it isevident that many minor changes may be made therein without departingfrom the spirit of this invention or the scope of the following claims.

I claim:

1. A melting furnace having tuyres, an air-preheating chamber within thefurnace, means for supplying air to the chamber from the exterior of thefurnace, a pipe extending from the air chamber through the wall of thefurnace, a windbox for distributing the alr from the said pipe to thetuyres, and an insulating jacket inclosing the windbox and the part ofthe said pipe disposed exteriorly of the wall of the furnace.

2. An air-case for use on the wall of a furnace, the said case beingperforated from its interiorly presented side to its exteriorlypresented side without effecting communication thereat to theinterior ofthe case.

3. A melting furnace having tuyres, an arcuate air case in the interiorof said furnace, said case having a curved outer wall and a corrugatedinner wall to compensate for the difference of expansion between thewalls, and means for conveying air from said air case to the tuyres.

4. A melting furnace having tuyres, an arcuate air case in the interiorof said furnace, said case having a curved outer Wall and a corrugatedinner wall to compensate for the difference of expansion between thewalls, stays connecting the inner and outer walls, and means forconveying air from said case to the tuyres.

5. A melting furnace having tuyres, an arcuate air case in the interiorof said furnace, said case having a curved outer wall and a corrugatedinner wall to compensate for the difference of expansion between thewalls, stays connecting the inner and outer walls, perforationsextending through the stays, and means for conveying air from said caseto the tuyres.

In testimony whereof I hereunto aflix my signature.

SAMUEL W. CRAWFORD.

